RC Gear Ratios Explained! Pinion and Spur for Max Performance

If you've already read our guide on how to make your RC car faster, you'll know that tweaking your gearing is one of the cheapest and most effective ways to change how your vehicle performs. Whether you want more top speed for tarmac runs or extra torque for crawling over rocks, it all comes down to two crucial components: the pinion and the spur.

While there are other gears in your car that dictate performance — like differential gears — the pinion and spur are the easiest to access and change on almost any chassis. Be warned, there is a bit of maths involved, but we'll keep it simple.

What Are Pinion and Spur Gears?

The pinion gear is the small gear attached directly to your motor's output shaft, while the spur gear is the larger gear that the pinion drives. The spur is usually integrated with a slipper clutch or a centre differential, but the concept of how they interact remains exactly the same across different setups.

How Do You Calculate an RC Gear Ratio?

You can calculate your primary gear ratio by dividing the number of teeth on the spur gear by the number of teeth on the pinion gear. This number tells you how many times the motor must turn to rotate the spur gear once.

For example, if you have a pinion gear with 20 teeth and a spur gear with 100 teeth, you divide 100 by 20 to get 5. This gives you a ratio of 5:1. Your motor has to complete five full revolutions to make the spur gear complete just one.

If we swap that 20-tooth pinion for a 40-tooth version while keeping the 100-tooth spur, the new ratio becomes 2.5:1. The motor now only turns two and a half times to spin the spur once. Because the motor is doing less work to turn the drivetrain, your wheels will spin faster at the same motor RPM. The closer you get to a 1:1 ratio, the higher your theoretical top speed.

The Bicycle Analogy

Think of RC gearing like riding a mountain bike. If you start in 1st gear, your legs will be pedalling quickly, and it's effortless to get moving, but you won't reach a high top speed. That's a low gear ratio (e.g., a small pinion and large spur).

If you try to take off in 15th gear, it takes a massive amount of leg power to get the bike moving. Once you do, you'll be flying, but it requires serious effort. That's a high gear ratio (e.g., a large pinion and small spur).

How Gearing Changes Affect Performance

Changing your gear ratio is always a compromise. You cannot gain top speed without sacrificing acceleration and increasing the load on your electronics. Here is a quick reference guide on what to expect when you start swapping gears.

Managing Heat and Finding the Sweet Spot

It takes a lot of torque to push a heavy RC car using a fast gear ratio. If you push the gearing too far, you will overheat the motor, cook the ESC, and potentially damage your battery pack. Most manufacturers ship their cars with conservative gearing right out of the box.

For example, a factory 2WD Traxxas Slash with a brushed motor has a pinion-to-spur ratio of 5.625:1. When combined with the internal gearbox ratio, the final drive ratio is 15.3:1 — meaning the motor turns 15 times for every single rotation of the wheels. This is a safe baseline that keeps temperatures in check.

If you decide to gear up for speed runs, it is highly recommended to monitor your motor and ESC temperatures using an infrared temperature gauge. Finding the "sweet spot" means achieving your desired speed while keeping the electronics well within their safe operating limits.

Note: Installing massive pinions for speed runs can void the warranty on RTR electronics from brands like Traxxas. A 1/5-scale basher isn't designed to sit at 120 km/h constantly, so if you push the limits, expect the limits to push back.

Other Factors: Diff Gears and Wheels

While the pinion and spur are the most common ways to adjust gearing, other components affect your final drive ratio.

Differential Gears

Some manufacturers produce different ratio diff gear sets. These are especially popular in rock crawlers and drift cars to create "overdrive" setups, where the front or rear wheels are geared to spin slightly faster than the opposite end to help pull the car through tight turns or maintain a slide.

Tyres and Rollout

Swapping your wheels and tyres changes your final drive ratio without touching the gearbox. This is called "rollout" — the distance the car travels for every revolution of the motor. Upgrading a crawler from 1.9-inch tyres to larger 2.2-inch tyres increases the rollout. The car will cover more ground per motor rotation, acting exactly like installing a larger pinion gear. Always keep an eye on your motor temps when fitting larger, heavier wheels.

Ready to Re-Gear?

Whether you're chasing backyard speed records or trying to keep your motor cool during long bash sessions, getting your gear ratio dialled is a rewarding part of the hobby. To find the exact pinions and spurs that fit your specific model, punch your car's details into our Part Finder and explore our range of upgrade gears from top brands like Robinson Racing.